Height adjustment in a vehicle fitted with air suspension

ABSTRACT

A height sensor (20) of a height regulating device of an air spring suspension system of a vehicle is calibrated by using the air spring bellows (16) as jacks while the height regulation by the control device (44) is disabled. A dialog is set up between a test device (50) connected by an interface (52) with the control device (44), whereby the test device (50) takes over the control of the air supply to and from the air spring bellows (16) and the height of the vehicle body (10) is brought to a desired null height. The output (h n ) of the sensor (20) is then stored in a non-volatile memory and is used as a reference height (h o ) for the height regulation.

FIELD OF THE INVENTION

The invention relates to a method of calibrating a height sensor in anelectronically controlled height regulating device of an air springsuspension system of a vehicle. The invention includes an apparatus forcalibrating the height sensor.

BACKGROUND OF THE INVENTION

Hitherto, when calibrating the height sensor of an air springsuspension, it has been necessary first to bring the height of thevehicle body to a suitable reference height, that is to say, the desiredheight. This entails the use of a lifting device, such as a vehiclehoist, a lifting platform or under-frame blocks. The height sensor isthen adjusted, for example, by adjusting its fixing, until it deliversthe correct electrical value associated with that height. Such anexpenditure and measuring technique do not lend the method to massproduction techniques.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a calibration method whichdoes not require any additional mechanical appliances for it to becarried out.

This object is met by the calibration method of the invention. Accordingto a feature of the method of the invention, the height regulatingfunction is disabled and the air springs are controlled externally tobring the body height to a desired null position whereafter the heightsensor reading (h_(n)) for this null position is programmed into theregulating device to serve as a reference value or an initial referencevalue for the height regulation. The air spring suspension is itselfused as a mechanical jack for raising or lowering the vehicle body to adesired height at which adjustments may be made.

It is only necessary for the height sensor to be fixed in a roughlyadjusted position as the final calibration can be effected purelyelectronically. Thus, the height sensor is secured in a roughly adjustedposition after the vehicle body is brought to the desired null positionand before the height sensor reading is programmed into the regulatingdevice.

The extreme limits between which the height adjustment may be made canbe established by programming the null position into the regulatingdevice. The vehicle body is then raised by using the air springs untilthe air springs are fully expanded and the corresponding height sensorreading is programmed into the regulating device as a maximum heightvalue. Also, and after programming the null position into the regulatingdevice, the vehicle body is lowered by using the air springs until thebody is resting on its stops and the corresponding height sensor readingis programmed into the regulating device as a minimum height value.

The commands for carrying out the method can be entered into theelectronic control device of the height regulating device by plugging ina separate test device. Alternatively, an existing remote control can beadapted or programmed to carry out the calibration.

The invention includes apparatus for calibrating a height sensor in aheight regulating device of an air spring suspension system of avehicle.

The reference signal, or a signal from which the reference signal may bederived, is preferably stored in a non-volatile memory.

One embodiment of the apparatus comprises a test device and such a testdevice can be a small commercially available computer.

In another embodiment, a conventional remote control can be programmedto be used as such a test device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described, by way of example, with reference tothe accompanying drawing, in which:

FIG. 1 is a diagram of an air suspension system for a vehicle fittedwith a height regulating system; and

FIG. 2 is a block diagram of the height regulating system andcalibrating apparatus in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows diagrammatically a part of a vehicle body 10 attached to anaxle 12 by an air suspension 14. The air suspension 14 comprises an airspring bellows 16 and a height measuring sensor 20, each arrangedbetween the vehicle body 10 and the axle 12. The height measuring sensor20 can be a simple potentiometer or variable resistor. The air springbellows 16 is filled and emptied as required by a compressed airreservoir 22 and a solenoid valve arrangement 24. The reservoir 22 ischarged from a compressor (not shown) via a line 26 containing anon-return valve 28. The valve arrangement 24 comprises a 3-port,2-position valve 30 and a 2-port, 2-position valve 32 in a line 34between the reservoir 22 and the suspension bellows 16. The valves arespring-biased to their positions shown and are operated by solenoids36,38. Actuation of both valves 30,32 connects the air spring bellows 16to the reservoir 22 in order to feed compressed air to the airsuspension 14 and thereby increase the height h of the vehicle body 10relative to the axle 12. Actuation of the valve 32 alone connects theair spring bellows 16 via the unactuated valve 30 to exhaust and therebydecrease the height h of the vehicle body 10.

The height sensor 20 is connected to a comparator 40 whose output isconnected to a computer 44. The computer controls the valve solenoids36,38 via end stage amplifiers 46,48. The computer 44 compares theactual body height h with a desired value h_(o) and controlsenergization of one or both of the solenoids 36,38, whereby, upon adeviation of the body height h from the desired value, e.g., due to achange in load, compressed air is supplied to or air is released fromthe air spring bellows to raise or lower the body back to the desiredheight.

To calibrate the sensor 20, a separate test device 50 is plugged intothe control computer 44 at a serial data interface 52. The test device50 initiates a dialog and receives a synchronzing signal of the controlcomputer 44 and is then ready for further dialog.

By entering the command "calibration mode" into the test device 50, theregulating function of the control computer 44 is temporarily disabledand the test device 50 takes over the control of the valve solenoids36,38. Next the vehicle body is raised or lowered by entering suitablecommands into the test device 50 to adjust the height (h) of the vehiclebody to a null value h_(n) which is verified by physical measurement ofthe body height. Height signals from the height sensor 20 are not notedat this time. While the body is still in its null position, the sensor20 is secured in a coarsely adjusted position. The command "calibrate"is then entered in the test device 50, whereby the sensor reading h isfed to the control computer 44 and is stored as the null value h_(n) ina non-volatile memory 54 within the control computer 44. Thereafter, thecommand "end of calibration" is entered in the test device 50 and theregulating function of the control computer 44 is thereby reestablished.The null height reading h_(n) serves as the desired height h_(o) withthe actual height h is compared by the comparator 40.

The separate test device 50 could be a conventional personal computer, adesk top computer or a briefcase computer. Alternatively, it could beconstructed as a special piece of hardware. The test device 50 may havea standard interface, (for example, DIN V24 or RS 232C) by which it canbe connected to the control computer 44 via a level converter.

In the case of a vehicle, such as a lorry or heavy goods vehicle, fittedwith a remote control by means of which the normal height of the vehiclebody can be steplessly adjusted, there is the possibility of carryingout the calibration method of the invention without any additionalhardware. A diagnosis switch can be operated to enter the calibrationfunctions into the remote control. A feedback of the actual height ofthe vehicle body can be obtained by pilot lamps already fitted to thevehicle, such as "normal height lamp", "fault lamp".

We claim:
 1. A method of calibrating a height sensor in anelectronically controlled height regulating device of a multiple airspring suspension system of a vehicle, the method comprising the stepsof:disabling the height regulating function and externally controllingthe air springs to bring the body height to a desired null position;and, then programming said null position into the regulating device toserve as a reference value for the height regulation.
 2. The method ofclaim 1, wherein the height sensor is secured in a roughly adjustedposition after the vehicle body is brought to the desired null positionand before the height sensor reading is programmed into the regulatingdevice.
 3. The method of claim 1, wherein, after the null position isprogrammed into the regulating device, the vehicle body is raised byusing the air springs until the air springs are fully expanded and thecorresponding height sensor reading is programmed into the regulatingdevice as a maximum height value.
 4. The method of claim 1, wherein,after the null position is programmed into the regulating device, thevehicle body is lowered by using the air springs until the body isresting on stops thereof and the corresponding height sensor reading isprogrammed into the regulating device as a minimum height value.
 5. Themethod of claim 1, wherein an external test device is plugged into aserial data interface, with which the height regulating device isprovided, and an external computer is used to control the air springsand to enter the height sensor reading or readings into the regulatingdevice.
 6. The method of claim 1, wherein the vehicle is fitted with aremote control for the adjustment of the body height and the remotecontrol is programmed to carry out the calibration function.